Fair Value - Recurring Fair Value Measures (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Liabilities [Abstract]    
Activity in Level 3 $ (3.8)  
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value 2.1  
Available-for-sale Securities, Debt Maturities, After One Year Through Three Years, Fair Value 7.2  
Available-for-sale Securities, Debt Maturities, After Three Years Through Five Years, Fair Value 0.0  
Available-for-sale Securities, Debt Maturities, After Five Years, Fair Value 0.4  
Recurring Fair Value Measures [Member]    
Investments [Abstract]    
Available-for-sale – Equity Securities [1] 11.1 $ 12.2
Available-for-sale – Corporate and Governmental Debt Securities [1] 9.7 [2] 8.0
Cash Equivalents [1] 0.9 1.0
Total Fair Value of Assets 21.7 21.2
Liabilities [Abstract]    
Deferred Compensation 21.2 [3] 19.8 [4]
U.S. Water Services Contingent Consideration [4]   3.8
Total Fair Value of Liabilities 21.2 23.6
Total Net Fair Value of Assets (Liabilities) 0.5 (2.4)
Fair Value Hierarchy Transfers, All Levels 0.0 0.0
Recurring Fair Value Measures [Member] | Level 1 [Member]    
Investments [Abstract]    
Available-for-sale – Equity Securities [1] 11.1 12.2
Available-for-sale – Corporate and Governmental Debt Securities [1] 0.0 [2] 0.0
Cash Equivalents [1] 0.9 1.0
Total Fair Value of Assets 12.0 13.2
Liabilities [Abstract]    
Deferred Compensation 0.0 [3] 0.0 [4]
U.S. Water Services Contingent Consideration [4]   0.0
Total Fair Value of Liabilities 0.0 0.0
Total Net Fair Value of Assets (Liabilities) 12.0 13.2
Recurring Fair Value Measures [Member] | Level 2 [Member]    
Investments [Abstract]    
Available-for-sale – Equity Securities [1] 0.0 0.0
Available-for-sale – Corporate and Governmental Debt Securities [1] 9.7 [2] 8.0
Cash Equivalents [1] 0.0 0.0
Total Fair Value of Assets 9.7 8.0
Liabilities [Abstract]    
Deferred Compensation 21.2 [3] 19.8 [4]
U.S. Water Services Contingent Consideration [4]   0.0
Total Fair Value of Liabilities 21.2 19.8
Total Net Fair Value of Assets (Liabilities) (11.5) (11.8)
Recurring Fair Value Measures [Member] | Level 3 [Member]    
Investments [Abstract]    
Available-for-sale – Equity Securities [1] 0.0 0.0
Available-for-sale – Corporate and Governmental Debt Securities [1] 0.0 [2] 0.0
Cash Equivalents [1] 0.0 0.0
Total Fair Value of Assets 0.0 0.0
Liabilities [Abstract]    
Deferred Compensation 0.0 [3] 0.0 [4]
U.S. Water Services Contingent Consideration [4]   3.8
Total Fair Value of Liabilities 0.0 3.8
Total Net Fair Value of Assets (Liabilities) $ 0.0 $ (3.8)
[1]
Included in Other Non-Current Assets on the Consolidated Balance Sheet.
[2]
As of December 31, 2019, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $2.1 million, in one year to less than three years was $7.2 million, in three years to less than five years was zero and in five or more years was $0.4 million.
[3]
Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.
[4]
Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.